I'm guessing it is because commercial terms are sensitive. See...

I'm guessing it is because commercial terms are sensitive. See the previous announcement on this matter from Tawana 25 Oct 2018:

Bald Hill JV Tantalum Concentrate Sales: https://www.asx.com.au/asxpdf/20181025/pdf/43zlchp767c74d.pdf

Quote from previous announcement:
Tawana Managing Director Mark Calderwood said "Tawana and Alliance are pleased to have finalised the initial sales for its Bald Hill tantalite concentrate stockpiles with two of the world's leading suppliers of tantalum products. Tantalum pricing has been relatively strong in 2018 and we are encouraged by the level of interest in high quality tantalum concentrates with low levels of deleterious elements. Details of pricing is kept confidential at the request of the purchasers, however premium +30% Ta2O5 concentrates from Bald Hill command prices well in excess of those previously budgeted."